Massive Excavation Project Required No Vibrations From Construction

Kris Graham of United Rentals Trench Safety (URTS), provider of the shoring components, explains that the challenges began early in planning.

“An early issue was finding as-built plans of the Union Station Building,” says Graham. “D.H. Charles, design engineer for the beam and plate shoring system, needed to know if Union Station had a basement or whether the walls were built on a concrete footer and of what depth.

“After several weeks of searching, the needed as-built plans could not be found, so subcontractor Iron Woman hired a vacuum truck to do pot holing around the foundation. We found that Union Station had both basements and foundations on footers, depending on the section of the building and when it had been built. This information gave the engineers something to work with.

“The original design had our shoring pit approximately 20-feet from the front of Union Station. However, the cast iron awning that extended from the building did not give the caisson driller, excavator and the cranes enough room to work. The design pushed the pit out six feet, providing the minimum amount of clearance for the construction equipment.”

As work continued, a decision was made to change the size of the crane used for setting sections of the concrete in place for the storage tank.

“The original plan called for a crane smaller than the one used for excavation -- that would require repositioning several times during the setting of the concrete tank sections. At the last minute, a larger crane was substituted so that all the concrete tank sections could be set without needing to reposition the crane.”

The shoring design had calculated weight and sizes based on the smaller crane. D.H. Charles Engineering redid the calculations based on the size, weight and footprint of the outriggers, and needed to move the crane 18-feet away from the shored pit, where it would still be able to handle all the picks.

“United Rentals brought-in four, 1-inch thick, 8-by 20-foot steel road plates to place under the crane’s outriggers and distribute the weight over a larger area. The engineer developed a design that kept the adjacent street open and allowed the larger crane to be set up just once. This was all resolved in record time while the equipment, crews and precast concrete delivery trucks were at the job site.”